SARS, a dangerous, emerging respiratory disease caused by a corona virus (SARS-CoV), is a novel member of that RNA virus family. There is an urgent need to understand the pathogenesis, test antiviral and other therapeutic modalities, and develop prototype vaccines should the virus become a major epidemic threat. There are few human cases available for study in 2004, and unfortunately, there are no economical animal models in well-characterized species. We have followed up on the discovery of human angiotensin-converting enzyme 2 (ACE2) as the SARS receptor by cloning that gene and showing that transfection of non-permissive mouse cells with the ACE2 gene allows SARSCoV replication and CPE. We propose to develop transgenic mouse lines on a hybrid and two inbred backgrounds to attempt the elucidation of these important issues in a murine model. The gene will be introduced under control of the general vector/promoter pCAGGS/chicken beta actin. Animals will be selected on the basis of the presence of the ACE2 gene, levels of protein expression, and early testing of potential founders for responses to SARS-CoV infection. Positive results will be characterized as to expression of transgene at the RNA and protein levels. Hypotheses to be tested are 1) Expression of human ACE2 causes robust SARS-CoV replication and SARS-like disease in the mouse, and 2) Cytotoxic T cell response is critical in the resolution of the infection. Quantifiable markers for the infection and the disease will include viral titer, chemokine levels, and histopathology indices. In addition, distribution of viral antigens at the cellular (immunohistochemistry) and tissue levels (Western blot), viral infectivity, and cellular and humoral immune response will be assessed. Endpoints of infection will be weight loss and mortality. Comparison of these results to clinical data will be made. [unreadable] [unreadable] [unreadable]